A wide variety of methods and standards are known in the art for encoding information in a form that can be read by a computer using an image sensor or other type of optical sensor. The best-known standards of this sort are barcodes, including the traditional one-dimensional arrays of stripes and two-dimensional barcodes, such as QR codes. Other types of image-based computer-readable encoding schemes and symbols use color information, rather than the monochrome symbols provided by conventional barcodes.
For example, PCT International Publication WO 2013/182963, whose disclosure is incorporated herein by reference, describes a method for encoding information that includes specifying a digital value and providing a symbol comprising a plurality of polygons meeting at a common vertex and having different, respective colors selected so as to encode the specified digital value. The use of such symbols in the particular context of display synchronization is described in PCT International Publication WO 2015/083055, whose disclosure is likewise incorporated herein by reference.
As another example, PCT International Publication WO 2012/022678 describes a visual reference tag formed from an array of cells, wherein each cell is visually distinct from all other cells in a given neighborhood and each of said cells contains a single visual cue, for example a unique color, selected from a finite number of visual cues.